This invention relates to a heart-synchronized pulsed laser system, and more particularly to such a system which operates on a beating heart between the R and T waves of the electrocardiogram (ECG) signal, and to a handpiece for a medical laser system.
The heart muscle receives its blood supply from the coronary artery, which feeds out and around into the outside of the heart muscle. Some time ago it was noticed that reptilian hearts had no arterial supply to the heart muscle.
Rather, the reptilian heart blood supply was delivered through the inside wall of the heart directly to the heart muscle. The thought occurred that this could be an alternative to the heart bypass technique which can usually be applied to a patient no more than twice: after two bypass operations the risks outweigh the benefits and the patient is generally without further recourse. In an attempt to imitate the reptilian condition, tiny holes were made in mammalian hearts with hot wires or needles but this met with limited success. Although the holes healed from the outside and did allow for some internal blood delivery, the holes soon healed over entirely and cut off the blood supply. The protocol was then developed using a laser to make the holes and this met with much greater success. This technique is known as transmyocardial revascularization (TMR). However, the laser technique introduced a host of new problems. The heart is extremely sensitive to a laser pulse at certain times during its cycle. A laser pulse striking the heart at the T time of the ECG wave, for example, could cause the heart to fibrillate and result in heart failure. If the heart is stopped during the procedure this problem can be avoided. But stopping the heart requires cooling the heart and connecting the patient to a heart-lung machine with all the attendant increased risks that this brings including prolonged recovery times. A beating heart, on the other hand, is difficult to administer this technique to because as the heart contracts and expands the surface may not remain normal to the laser beam, the heart wall changes distance from the focus of the beam, and the thickness of the wall changes so that the positioning of the laser handpiece and the power of the beam required are varying and unpredictable. This makes precise location of laser beam on the heart difficult so that not only will the holes not be properly located, but other areas of the heart which should not be struck may well be struck. Further, when the technique requires stopping the heart the chest must be cut open including cutting the sternum, which is especially risky because the sternum is a primary source of red blood cells.
A beating heart is electrically active and the contact of a handpiece against the heart wall may disrupt that electrical activity and interfere with the heart function. Arrhythmia and fibrillation can occur and can result in heart failure. Further, any interference with the electrical field of the heart interrupts the synchronous operation of laser so that the laser is no longer constrained to fire at the optimum moment in the beating heart cycle. The current handpiece used with CO2 lasers have a relatively sharp tip on a gauge rod extending from the end of the handpiece used to consistently position the handpiece at the proper distance from the stilled heart wall for accurate laser beam focusing and impingement. Such a tip creates increased pressure on the heart, which can cause arrhythmia, fibrillation, and can even puncture the wall of the heart. Further, with these handpieces it is difficult to maintain the laser beam perpendicular with the wall of a beating heart as is necessary to effect clean, correctly placed holes in the heart wall. Finally, these handpieces may slide on the heart wall during the procedure disrupting the surgeon""s concentration.
It is therefore an object of this invention to provide a laser system for performing transmyocardial revascularization on a beating heart.
It is a further object of this invention to provide such a laser system which is synchronized to operate at a specific time in the heart""s beating cycle when accuracy is enhanced and risks are reduced.
It is a further object of this invention to provide such a laser system which is synchronized to operate between the R and T waves of the heart""s ECG.
It is a further object of this invention to provide such a laser system which provides shorter pulses that interfere less with the heart function and make cleaner holes.
It is a further object of this invention to provide such a laser system which times the laser pulses to occur when the heart surface is relatively stable to enhance the accuracy of laser aiming and focusing and minimize the risk of striking an undesirable part of the heart.
It is a further object of this invention to provide such a laser system which times the laser pulses to occur when the heart wall is at a point in its cycle when it is electrically least sensitive to interference with its functioning.
It is a further object of this invention to provide such a laser system which substantially reduces the chance of inducing fibrillation.
It is a further object of this invention which provides such a laser system which is safe, requires no attachment of the patient to a heart-lung machine, no cooling of the heart, and no opening of the sternum.
It is a further object of this invention to provide such a laser system which requires only a simple incision between the patient""s ribs and results in less trauma, faster recovery and less blood loss.
It is a further object of this invention to provide an improved laser handpiece for a laser system for transmyocardial vascularization.
It is a further object of this invention to provide such a laser handpiece which more readily maintains perpendicularity with the wall of a beating heart.
It is a further object of this invention to provide such a laser handpiece which accurately locates the laser beam focal point at the correct point on the heart wall.
It is a further object of this invention to provide such a laser handpiece which reduces interference with the heart electric field and function.
It is a further object of this invention to provide such a laser hand piece which prevents interference with or damage to the laser beam lens.
It is a further object of this invention to provide such a laser handpiece which prevents movement of the handpiece with respect to the heart wall.
The invention results from the realization that a pulsed laser system can be achieved for operating on a beating heart accurately, with minimal interference to the heart and minimal risk to the patient by synchronizing the pulsing of the laser to the ECG of the heart so that laser pulses can be administered to the heart only during the moment when the heart is most still, least sensitive electrically, during the period between the R and the T waves of the ECG.
This invention features a heart-synchronized pulsed laser system including a laser system. There are means for sensing the contraction and expansion of a beating heart which is to be synchronized with the laser. There are means, responsive to the means for sensing, for generating a trigger pulse in response to the ECG signal, as well as means for positioning the leading edge of the trigger pulse during the contraction and expansion cycle of the heartbeat, and means for defining the width of a trigger pulse to occur during the heartbeat cycle. There are means responsive to the trigger pulse for firing the laser to strike the beating heart at the selected time indicated by the trigger pulse position and for the period indicated by the width of the trigger pulse.
In a preferred embodiment, the means for sensing the contraction and expansion includes means for sensing the ECG signal of the beating heart. There is a laser delivery system which may include an articulated beam delivery arm or a fiber optic element. The means for sensing the ECG signal of the beating heart may be an ECG unit and the means for generating the trigger pulse may do so in response to the R wave of the ECG. In the means for positioning, the leading edge of the trigger pulse may position the trigger pulse between the R and the T waves of the ECG. The means for defining the pulse width of the trigger pulse may define a pulse width which occurs in the period between the R and the T waves of the ECG.
The means for generating may include a marker pulse circuit for generating a specific time in a heartbeat cycle of the ECG for providing a marker pulse representative of that time. The means for generating may further include a trigger pulse circuit responsive to the marker pulse circuit for providing a trigger pulse whose position in the heartbeat cycle is a function of the specific time in the cycle represented by the marker pulse. The trigger pulse circuit may include means for delaying the marker pulse to locate it at a selected position relative to its initial position in the heartbeat cycle, and means for adjusting the duration of the marker pulse to a selected time to create the trigger pulse of the selected position and width.
The means for firing may include gate means for inhibiting delivery of the trigger pulse to the laser and may further include switch means for enabling the gate means to deliver the trigger pulse to the laser. There may be an arming circuit for further inhibiting delivery of the trigger pulse to the laser, and arming switch means for enabling the arming circuit to deliver the trigger pulse to the laser.
The handpiece of this invention results from the realization that an effective and safe handpiece capable of contacting the wall of the beating heart to insure proper location and focus of the laser beam, yet minimize danger to or interference with the beating heart, can be achieved by focusing the laser beam in the vicinity of the laser beam exit aperture at the end of the handpiece and providing a large, flat, knurled heart contact surface at the end of the handpiece and providing a large, flat, knurled heart contact surface at the end of the handpiece to minimize pressure on and interference with the beating heart and also to prevent movement of the contact surface with respect to the heart.
This invention features a handpiece for use in a medical laser system such as a transmyocardial revascularization heart-synchronized pulsed laser system as disclosed in U.S. Pat. Nos. 5,125,926 and 5,109,388.
The handpiece includes a barrel having a passage for transmitting a laser beam. A contacting wall is located on one end of the barrel to be positioned against the heart wall. The contacting wall includes an aperture in communication with the laser beam passage in the barrel. The contacting wall includes a solid face extending radially outward from the aperture to the periphery of the contacting wall providing a broad, flat contact surface for the handpiece which does not interfere with the function of the heart during the medical procedure and which stabilizes the handpiece on the heart wall. The contacting wall includes a knurled surface for preventing movement of the contacting wall with respect to the heart wall during surgery.
The barrel may include a window proximate the contacting wall and a finger grip along the length thereof to assist the surgeon in viewing the lasing site and to provide a firm grip during surgery.
The barrel may be straight or angled and include reflecting means such as a mirror. Also, a lens focusing unit may be included to focus the laser beam proximate the aperture, beyond the aperture, within the barrel, or in the aperture.